Lithium-ion secondary batteries comprise positive and negative electrodes capable of reversibly storing and releasing lithium ions and an electrolyte sandwiched between the two electrodes, and are charged and discharged when lithium ions in the electrolyte move back and forth between the electrodes. They are popular as power sources for various portable devices and the like because they provide high energy densities with light weight. They are also promising in areas requiring large-capacity power sources, such as hybrid vehicles, electric cars and the like, and further improvements in safety and durability are expected. Patent Literature 1 and Patent Literature 2 are examples of technical literature relating to various improvements in the performance of lithium-ion secondary batteries.